Mohammed Chatbi

Nano-silica can stiffen cementitious composites, but its benefit depends on how well the nanoparticles are dispersed, and agglomeration is common in the alkaline pore solution of cement paste. This study presents an analytical framework for the free vibration of SiO₂ nanoparticle-reinforced concrete beams resting on a Winkler–Pasternak elastic foundation, with nanoparticle agglomeration explicitly incorporated into the effective properties. Agglomeration is described by two parameters: the volume fraction of nanoparticle-rich inclusions, ξ, and the fraction of nanoparticles located within them, ζ. These parameters enter a two-stage homogenization scheme that combines a Voigt–Reuss estimate for each region with Paul’s model for the composite, and their admissible range is derived from the volume-fraction constraints. The resulting properties are embedded in a three-unknown higher-order shear deformation theory that satisfies the traction-free surface conditions without a shear correction factor. The governing equations are derived from Hamilton’s principle and solved analytically for simply supported, clamped–clamped and clamped–simply supported beams. The beam formulation agrees with published benchmarks for functionally graded beams to within 0.03% without a foundation and 0.6% on a Winkler–Pasternak foundation. For a fixed matrix and hydration state, increasing the SiO₂ volume fraction from 0 to 0.20 raises the fundamental frequency by about 14% for all three boundary conditions. This gain comes almost entirely from stiffening, since the change in density contributes less than 1%. When half of the nano-silica is agglomerated and does not contribute to load transfer, this gain falls to about 8%, so roughly half of the dynamic benefit is lost. Over the investigated range of dimensionless foundation stiffness, the Pasternak parameter raises the frequency more than the Winkler parameter, and clamped–clamped beams give the highest frequencies, followed by clamped–simply supported and simply supported beams. The framework links dispersion quality, boundary restraint and foundation support to the dynamic response of nano-engineered concrete members.

Saharan ksour are undergoing a profound transformation as urbanization spreads, building practices change, and old functions give way to new ones. Their architecture and building materials have been studied extensively. What has not been documented is how these pressures reshape the spatial relations that bind a historic core’s parts together. This matters because it is morphological continuity, not architectural fabric alone, that keeps a historic settlement legible once it is absorbed into a modern city. This study addresses that gap through a diachronic morphological reading of the Ksar of Béchar, in southwestern Algeria. It traces seven structuring components, the perimeter wall (Essour), defensive towers (Bordjs), gates (Bâb), the alley network (droub), collective open spaces (Rahbas/Nouader), the El Masdjid El Atik mosque, and the housing stock, across more than a century of change. The analysis draws on a triangulated corpus of historical archives, redrawn historic plans, archival photographs, 1952 and 1962 aerial imagery, recent satellite imagery, field observations, and testimonies from long-standing residents. Rather than comparing historical and current states at the level of individual components alone, the relational reading combines two analytical levels: it traces the differentiated trajectories of the seven components while simultaneously examining the persistence, transformation, and recomposition of the spatial relations between them across documented temporal states. This relational analysis reveals two differentiated morphological trajectories and one cross-cutting process. The defensive envelope (Essour, Bordjs, Bâb) has fragmented and largely disappeared. The internal structures (droub, Nouader, the mosque, housing) show strong spatial permanence beneath their architectural and functional change. And across all seven components, spatial relations have been recomposed as a system, progressively opening the once-enclosed core to the surrounding city. The Ksar of Béchar’s evolution is therefore neither integral conservation nor outright erasure. It is a relational recomposition in which peripheral, boundary-defining elements erode while internal structuring relations persist. Beyond this case, the study offers a transferable, source-triangulated analytical framework for reading morphological recomposition in Saharan and other vernacular historic settlements, one directly usable in heritage conservation and historic urban landscape management strategies.

Rapid urban expansion in arid intermediate cities often produces fragmented urban structures that exacerbate inequalities in public transport accessibility and hinder sustainable mobility. However, the relationships between urban fragmentation, transport accessibility, and travel behavior remain insufficiently explored in pre-Saharan cities. This study investigates these interactions through the case of El Bayadh, Algeria, using an integrated methodology combining urban morphological analysis, Geographic Information Systems (GIS), a household survey of 577 households, traffic counts, institutional interviews, and spatial equality assessment based on the Gini coefficient. Public transport accessibility was evaluated using a 300 m walking threshold, complemented by sensitivity analyses at 400 m and 500 m. The results indicate that approximately 65% of the population lives within 300 m of a bus stop, although coverage is strongly concentrated in central districts. A Gini coefficient of 0.41, provided by the El Bayadh Directorate of Transport and computed across 20 urban zones, indicates moderate-to-high spatial inequalities in accessibility that persist despite increasing the service threshold, suggesting that these disparities are more closely associated with urban fragmentation than with the specific walking-distance threshold used to define service coverage. The transport network comprises 11 bus routes, approximately 160 bus stops, and 90 km of routes; however, limited service quality and uneven spatial distribution contribute to a high dependence on private transport, with 45% of trips made by private car, 35% by taxi, and only 20% by bus. These findings are consistent with accessibility inequalities arising from the mismatch between fragmented urban morphology, centralized urban functions, and the configuration of the public transport network. The proposed framework provides transferable insights for planning more equitable and sustainable mobility systems in rapidly urbanizing arid intermediate cities.

This study investigates the influence of curing conditions on mechanical performance, residual strength after high-temperature exposure, and microstructural evolution of geopolymer mortars based on ceramic sanitaryware waste (CSW). Direct and delayed thermal curing regimes were applied at 60 °C and 80 °C for 48 h and 72 h. The fresh mixtures exhibited adequate workability with a flow diameter of 21 cm, indicating suitable consistency for casting. Results show that direct curing consistently enhances compressive strength, reaching 30.97 MPa at 80 °C for 72 h, compared with 15.88 MPa under delayed curing. Increasing curing temperature and duration improved early-age mechanical performance, particularly under direct curing conditions. After exposure to 800 °C, directly cured specimens retained higher residual compressive strength, with an improvement of approximately 6.6% compared with delayed-cured specimens. Microstructural characterization using scanning electron microscopy coupled with energy-dispersive spectroscopy and X-ray diffraction supported the observed mechanical trends under different curing conditions. The findings highlight the role of curing strategy in optimizing CSW-based geopolymer mortars for construction applications where mechanical performance and high-temperature resistance are required.

This study presents an analytical investigation of the dynamic behavior of concrete beams reinforced with different types of nano-clay (NC) particles and resting on a Winkler–Pasternak elastic foundation. The equivalent elastic properties of the nanocomposite were determined using an Eshelby-based homogenization model. An improved quasi-three-dimensional beam theory was applied to formulate the governing equations of motion, which were subsequently then analytically solved using Navier’s method. The analysis shows that NC reinforcement systematically elevates the natural frequencies of the beam, with the magnitude of improvement varying by particle type and concentration. Increasing the NC volume fraction to 30% leads to a significant rise in the fundamental frequency, reaching about 30% for hectorite (SHca-1) compared with the unreinforced beam, whereas montmorillonite (SWy-1) produces a more moderate increase of approximately 13%. This reinforcing effect remains consistent across different span-to-depth ratios, indicating that the influence of nano-clay content on the dynamic response is largely independent of beam slenderness. Furthermore, increasing the Winkler foundation stiffness results in an almost linear rise in frequency of approximately 18–22%, whereas the Pasternak shear parameter produces a stronger effect, reaching around 25% enhancement depending on the reinforcement type. These results indicate that incorporating nano-clay platelets can be an effective strategy for enhancing the vibrational stiffness of concrete beams and improving their dynamic performance when interacting with supporting soil media.

1. The demand for lightweight, high-stiffness structural components continues to grow across aerospace, marine, and high-performance engineering sectors, where structural efficiency, reliability, a...

The integration of silica nanoparticles (NS) into cementitious composites has emerged as a promising strategy to refine the microstructure and enhance concrete performance. Beyond their chemical role in accelerating hydration and promoting additional C–S–H gel formation, silica nanoparticles act as physical fillers, reducing porosity and improving interfacial bonding within the matrix. These dual effects result in a denser and more resilient composite, whose mechanical and dynamic responses differ from those of conventional concrete. However, studies addressing the vibrational and modal behavior of nano-reinforced concretes, particularly under elastic and viscoelastic foundation conditions, remain limited. This study investigates the dynamic response of NS-reinforced concrete slabs using a refined quasi-3D plate deformation theory with five (05) unknowns. Different foundation configurations are considered to represent various soil interactions and assess structural integrity under diverse supports. The effective elastic properties of the nanocomposite are obtained through Eshelby’s homogenization model, while Hamilton’s principle is used to derive the governing equations of motion. Navier’s analytical solutions are applied to simply supported slabs. Quantitative results show that adding 30 wt% NS increases the Young’s modulus of concrete by about 26% with only ~1% change in density; for simply supported slender slabs, this results in geometry-dependent increases of up to 18% in the fundamental natural frequency. While the Winkler and Pasternak foundation parameters reduce this frequency, the damping parameter of the viscoelastic foundation enhances the dynamic response, yielding frequency increases of up to 28%, depending on slab geometry.

Urban planning in arid climates must overcome numerous nonclimatic constraints that often result in outdoor thermal discomfort. This is particularly evident in Béchar, a city in southern Algeria known for its long, intense summers with temperatures frequently exceeding 45 °C. This study investigates the influence of urban morphology on thermal comfort and explores architectural and digital solutions to enhance energy performance in buildings. This research focuses on Béchar’s city center, where various urban configurations were analyzed using a multidisciplinary approach that combines typomorphological and climatic analysis with numerical simulations (ENVI-met 3.0 and TRNSYS 16). The results show that shaded zones near buildings have lower thermal loads (under +20 W/m²), while open areas may reach +100 W/m². The thermal comfort rate varies between 22% and 60%, depending on wall materials and occupancy patterns. High thermal inertia materials, such as stone and compressed stabilized earth blocks (CSEBs), reduce hot discomfort hours to under 1700 h/year but may increase cold discomfort. Combining these materials with targeted insulation improves thermal balance. Key recommendations include compact urban forms, vegetation, shading devices, and high-performance envelopes. Early integration of these strategies can significantly enhance thermal comfort and reduce energy demand in Saharan cities.

This research aims to study the effect of glass nanoparticles on improving the mechanical properties of the elastic modulus of concrete. By relying on the Mori-Tanaka model, the elastic modulus is determined based on added volume ratios ranging from 0% to 30%, and the results are compared with an experimental model. The main goal of this comparison is to align theoretical results with reality, allowing researchers to use these models in the future to predict the impact of concrete additives before beginning laboratory experiments, thus saving time and reducing costs. This study uses glass as an additive due to its high silica content and as a means of recycling glass in civil engineering, supporting environmental preservation and ecological sustainability and The Z. Hashin and S. Shtrikman model predicts the mechanical properties of nano-glass-reinforced eco-concrete, aiding sustainable construction by recycling glass waste. It shows performance improvements up to 30% glass addition before experimental validation.

In building construction, thermal comfort is a critical factor as it directly influences occupants' well-being, productivity, energy efficiency, and sustainability objectives. The maintenance of optimal thermal conditions not only enhances comfort but also contributes to reduced energy consumption. Concrete, being a primary material used in construction due to its economic, environmental, and ecological advantages, plays a significant role in achieving these thermal comfort goals. This chapter explores the thermal properties of organic concrete, a composite material incorporating Rogue straws. Employing LIWES and NIELSON SPAR models, the study assesses the homogeneous conductivity of different organic fiber fractions, thermal resistance, and flow characteristics. The findings demonstrate that organic concrete offers commendable thermal insulation suitable for construction purposes, emphasizing the significance of optimizing energy efficiency in construction technology.